This is a K23 Career Development Award resubmission of the application 1 K23 MH082114-01A1. My career development goals are to undergo training to learn: 1) treatment trials research design, methods, statistical analysis and ethical conduct; 2) the efficacy of bright light therapy for Bipolar Disorder (BD); 3) biological rhythms and symptom expression in BD. In my research plan, I propose a randomized controlled trial to examine the efficacy of bright vs. inactive light treatment for bipolar depression. The K23 Award will provide me skills, experience and pilot data to build an independent clinical research career. The specific aims are to randomize patients to active vs. inactive light and assess: 1) change in depressive symptom levels (SIGH-ADS; Williams et al, 2003), 2) the proportion that respond and remit; 3) durability of response (time to relapse, time to response, time to remission). The hypotheses are: 1) greater improvement in depression will occur with active vs. inactive light between Weeks 0 and 6; 2) a greater proportion of patients randomized to active vs. inactive light will respond (at least a 50% reduction on the baseline SIGHADS for 2 weeks or more) and remit (SIGHADS of 8 or less, for 3 weeks or more); 3) responders to active vs. inactive light will have the most enduring response. Significance. This is a treatment trial to explore an innovative, novel somatic intervention for bipolar illness. The proposal addresses the NIMH priority to develop effective depression treatments for BD. My K23 application builds upon my published pilot data of a robust antidepressant response to Midday Light Therapy in Women with Bipolar Depression (Sit et al, 2007). I will examine the outcomes in men and women and compare the efficacy of active light with a plausible placebo control. Design. Subjects are randomized to active (7000 lux) or inactive (50 lux dim red) light. The light dose is titrated to efficacy over 6 weeks in the acute phase. The pilot findings informed the timing and titration of the light dose. Subjects begin 15 minutes midday active or dim red light daily in Week 1; the dose advances by 15 minutes each week to a maximum 60 minutes daily by Weeks 4-6. Responders are followed for 18 weeks in the continuation phase to assess durability of response.